I originally opened https://bugs.kde.org/show_bug.cgi?id=380846, and hadn't done enough investigation. I orignally blamed screen corners, as I thought disabling them had fixed it.

I retested, and found a consistent way to reproduce the issue, and tested this both on the X implementation, and the Wayland implementation. I could reproduce this on the X implementation, not the Wayland implementation -- so that's a plus, at least for the future.

To reproduce the issue:
- Download xonotic: http://xonotic.org/
- Join a server and find a hit scan weapon (tested with the Machine Gun & Hagar)
- Hold down left click to start shooting and turn continously left
- Release the left mouse button

Expected behavior:
- The gun stops firing

Actual behavior:
- The gun continues to fire like you never let go of the left click button

Additional notes:
There's a similar issue with the right click button -- where it acts like it's continuing to be held down -- however, I suspect whatever is causing this for left click, is causing it for right click.

I can confirm that this has only happened for me since the update to 5.10, this did not happene before tumbleweed updated to 5.10 from 5.9.

Additional wayland note:
While Xonotic gameplay worked, after leaving Xonotic I was unable to move the mouse.